The present invention relates to a brake system of a vehicle, and more particularly, to a hydraulic pressure control apparatus for a brake system of a vehicle.
Recent progress in the field has provided vehicles with a distance control system for automatically controlling a distance to a vehicle ahead. Such a distance control system must include an apparatus, that is, a brake system, for reducing the speed of a vehicle, and a variety of brake systems have been investigated.
Typically, a brake system for a distance control system utilizes a hydro-vacuum apparatus, where the hydro-vacuum apparatus generates, or more specifically amplifies, hydraulic pressure for braking owing to pressure difference between a surge tank and atmosphere. A solenoid valve is adopted to control a consequent deceleration of the vehicle according to control of an electronic control unit. Such a brake system using a hydro-vacuum apparatus usually shows slow response and bad precision because the surge tank pressure depends on various circumstantial factors.
Another type of brake system provided with a hydraulic control apparatus between a master cylinder and a brake cylinder of a wheel has also been developed.
However, such a type of brake system has an excessively complicated hydraulic line structure because of many electrically controlled solenoid valves and check valves, and therefore its control logic is also much too complicated.
The present invention provides a hydraulic pressure control apparatus for a brake system of a vehicle where hydraulic pressure supplied to a brake cylinder of a wheel is more mechanically controlled, such that reliability of hydraulic pressure control is improved and cost of manufacturing the brake system is reduced. According to one embodiment of the present invention, a hydraulic pressure control apparatus for a brake system of a vehicle includes a control unit for controlling operation of the hydraulic pressure control apparatus, a pressurized fluid generating unit for pressurizing brake fluid and supplying the pressurized fluid, and a hydraulic pressure distributing unit for mechanically selecting and transmitting at least one of hydraulic pressure of the pressurized fluid supplied from the pressurized fluid generating unit and hydraulic pressure supplied from a master cylinder of the brake system to a wheel brake cylinder of the brake system.
The hydraulic pressure distributing unit preferably includes a pressure chamber for receiving pressurized fluid from the pressurized fluid generating unit; a distributing chamber adjoining the pressure chamber, to which a master cylinder is connected by a first port and a brake cylinder is connected by a second port; and a spool disposed in the distributing chamber for transmitting hydraulic pressures of the pressure chamber and the master cylinder to the second port.
The spool is operated by pressure of the pressure chamber and an elastic force of a first elastic member abutted against an inside portion of the distributing chamber. A first hole communicating with the first port and a second hole selectively communicating with the second port are formed at the spool. A check valve is disposed at the second hole such that the selective communication between the second hole and the second port is controlled by the check valve.
The check valve may be realized by including a second spring abutted against an inside portion of the distributing chamber, a valve seat connected to the second spring for selectively opening the second hole, and a valve stem connected to the valve seat and penetrating the second hole. A hollow space is formed inside the spool, and a stopper is disposed in the hollow space for limiting a moving distance of the check valve.
The pressurized fluid generating unit may be realized by including a pressurized fluid generator for pressurizing fluid supplied from the master cylinder under control of the control unit, and a hydraulic-input control valve unit for controlling supply of the pressurized fluid of the pressurized fluid generator to the hydraulic pressure distributing unit through a hydraulic input line.
The pressurized fluid generator may include a motor driven by control of the control unit and a hydraulic pump driven by the motor.
The pressurized fluid generating unit preferably includes an accumulator for accumulating the pressurized fluid supplied from the pressurized fluid generator, a first pressure detector for detecting hydraulic pressure of the pressurized fluid supplied from the pressurized fluid generator to the hydraulic-input control valve unit, and a second pressure detector for detecting hydraulic pressure of the pressurized fluid supplied from the hydraulic-input control valve unit to the hydraulic pressure distributing unit.
The hydraulic-input control valve unit preferably includes a first hydraulic-input control valve and a second hydraulic-input control valve, where the first hydraulic-input control valve is disposed in the hydraulic pressure distributing unit on a hydraulic input line, the hydraulic input line communicating the pressurized fluid generator and the hydraulic pressure distributing unit, and the second hydraulic-input control valve is disposed in the pressurized fluid generator on the hydraulic input line. The first hydraulic-input control valve is preferably normally open and the second hydraulic-input control valve is preferably normally closed. The pressurized fluid generator unit further includes a hydraulic exhaust control valve for controlling exhaust of brake fluid from the hydraulic input line, and the hydraulic exhaust control valve is preferable normally open.
According to an alternative preferred embodiment, a brake system of the invention includes a master cylinder actuated in response to driver manipulation of a brake pedal. A plurality of wheel cylinders communicate with the master cylinder. A hydraulic pressure generating unit is provided separate from and in addition to the master cylinder. A control unit communicates with the hydraulic pressure generating unit to signal the generating unit to generate hydraulic pressure. A distributing unit communicates with the master cylinder, the hydraulic pressure generating unit and the wheel cylinders to distribute fluid there between. The wheel cylinders communicate with the master cylinder through the distributing unit and the distributing unit selectively provides hydraulic pressure to the wheel cylinders from one or both of the master cylinder and hydraulic pressure generating unit in response to user manipulation of the brake pedal and signals from the control unit.
In a further preferred embodiment, the distributing unit comprises a body defining a cavity. At least one piston member is disposed in the cavity to define a pressure chamber at one side of the piston member and a distributing chamber at an opposite side of said piston member. The hydraulic pressure generating unit communicates with the pressure chamber to provide pressurized hydraulic fluid thereto and the master cylinder communicates with the wheel cylinders through the distributing chamber. Additionally, an elastic member is disposed in the distributing chamber acting on the piston member in opposition to hydraulic pressure in the pressure chamber supplied by the generating unit. By this arrangement, hydraulic pressure to the wheel cylinders from the distributing chamber may be varied by changing pressure in the pressure chamber with the hydraulic pressure generating unit.
Further, the at least one piston member preferably defines an internal space through which the master cylinder communicates with the distributing chamber. A check valve is then preferably disposed between this internal space and the distributing chamber to control hydraulic fluid flow there between in response to the piston member position in the distributing chamber. More preferably, the distributing unit includes first and second piston members, distributing chambers and check valves disposed symmetrically around a central pressure chamber.
According to another preferred embodiment the pressure generating unit comprises a hydraulic pump with an inlet and an outlet. A first fluid line from the outlet communicates with the distributing unit. At least one supply control valve is disposed in the first fluid line to control fluid flow from the pump to the distributing unit. A second fluid line communicates between the distributing unit, the pump inlet and a fluid reservoir associated with the master cylinder. Preferably, at least one exhaust control valve is disposed in the second fluid line to control fluid flow from the distributing unit. More preferably, the second fluid line comprises a fluid exhaust line and a pump supply line. The fluid exhaust line communicates with the first fluid line between the at least one supply control valve and the distributing unit. The pump supply line communicates between the exhaust line and the pump inlet. Preferably, the at least one exhaust control valve is disposed in the fluid exhaust line between the first fluid line and the pump supply line. Also preferably, two fluid control vales are disposed in the first fluid line between the pump and the distributing unit.